我试图将两个表相加，然后从另一个表中减去一个表。 H

Question

我正在尝试将两个表相加并从另一个表中减去一个。通过查询，我可以将两个表相加，但无法减去它们。正在 Postgres 中尝试以下是表格：

 memberid   ticker  numshares   purchasedate    transactionid   purchaseprice
7   aapl    1   Jun 28, 2017    22  146
7   aapl    1   Jun 28, 2017    23  146
7   hog     1   Jun 28, 2017    24  55
7   aapl    10  Jun 28, 2017    25  1458
7   aapl    2   Jun 28, 2017    26  292
7   aapl    3   Jun 28, 2017    27  437
7   aapl    5   Jun 28, 2017    28  729

这是销售表：

memberid    ticker  numshares   selldate    sellid  sellprice
7   aapl    10  Jun 28, 2017    4   1458
7   aapl    15  Jun 29, 2017    5   2154

更新：我得到了一切工作除了一个细节与以下 Postgres 声明：

`select qbuys.ticker, qbuys.total_purchaseprice-qsells.total_sellprice 
as current_total, qbuys.total_purchaseshares-qsells.total_sellshares as 
current_shares
from
(select sells.ticker, sum(numshares) as total_sellshares, 
sum(sellprice) as total_sellprice
from sells
where memberid = 7
group by ticker) as qsells, (select stocks.ticker, sum(numshares) as        
total_purchaseshares, sum(purchaseprice) as total_purchaseprice from 
stocks 
where memberid = 7
group by ticker) as qbuys
where qbuys.ticker=qsells.ticker`

剩下的唯一问题是，这不会返回没有相应销售的购买。只有在每张桌子上都有相同代码的买入和卖出时，它才会吐出总数。所以我需要的更新是让这个没有相应销售的购买吐出。

Answer 1

您需要连接两个表才能从另一列中减去一列的总和。

SELECT
a.ticker
,sum(a.numshares) as Total_Sell_Shares
,sum(a.sellprice) as Total_Sell_Price
,sum(a.numshares) - sum(b.numshares) as Total_Shares
,sum(a.sellprice) - sum(b.purchaseprice) as Total_Price
FROM Sells A
JOIN Stocks B on a.ticker = b.ticker
GROUP BY a.ticker

Answer 2

首先，带有数据的示例架构（在 postgres 中）：

derek=# create table t1 (ticker varchar, numshares integer);
CREATE TABLE
derek=# create table t2 (ticker varchar, numshares integer);
CREATE TABLE
derek=# insert into t1 values ('aapl',10);
INSERT 0 1
derek=# insert into t1 values ('aapl',5);
INSERT 0 1
derek=# insert into t2 values ('aapl',3);
INSERT 0 1

然后诀窍是对每个聚合函数使用内部查询：

derek=# select t1a.ticker, buys, sells, buys-sells as position 
from (select ticker, sum(numshares) as buys from t1 group by ticker) as t1a 
join (select ticker, sum(numshares) as sells from t2 group by ticker) as t2a 
on t1a.ticker=t2a.ticker;
 ticker | buys | sells | position 
--------+------+-------+----------
 aapl   |   15 |     3 |       12
(1 row)

Answer 3

我会尝试这样的事情。你怎么看？

select stocks.ticker, sum(stocks.numshares) - sum(sells.numshares) as total_shares, 
        sum(stocks.purchaseprice) - sum(sells.sellprice) as total_price 
from stocks 
left join sells
    on stocks.ticker = sells.ticket
where stocks.memberid = 7
group by stocks.ticker;